1. Field of the Invention
The present invention relates to an apparatus for inputting a character, and more particularly, to an apparatus and method for searching a handwritten memo, which is input by a user using a digital pen interface, for a word corresponding to the user's query. The digital pen interface is an interface in which a traditional method of writing down on paper with a pen is implemented in a digital form using an apparatus such as a touch screen which senses a pressure or an electrical signal of a pen-type device contacting a screen and detects a motion trace of the pen-type device in an electronic form.
2. Description of the Related Art
In recent years, development of digital technology has brought a rapid prevalence of digital devices. One consequence of such development is that attempts at development of advanced devices are being made in various aspects, including miniaturization and reduced weight. In particular, increased portability of a keyboard and mouse interface, which has been in widespread use as an interface for digital devices over the several decades, together with the miniaturized digital devices, has become a critical issue. A need for substitute interfaces to solve this problem has been growing with each passing year, and a substitute interface using a voice, a pen, a gesture, and video has been continuously researched and developed. Particularly, it has been common to use pen or voice as a communication interface in society for several thousands of years due to spontaneity and great potential in expression.
A digital pen interface is an approach of applying a communicative habit of writing down characters, figures, symbols, etc. on paper with a pen, to a digital device. To digitize a pen interface, character recognition technology has been continuously researched. Character recognition technology is a technique of recognizing character information (hereinafter, referred to as “ink”) input with a digital pen using a pattern recognition technique and converting the ink into an ASCII code used to express characters in a computer.
However, the character recognition technology is not widely spread as compared to the amount of research due to two major reasons. One reason is that character recognition speed is very slow. In order to allow a user to naturally perform writing (e.g., note-taking), recognition and processing need to be performed without a time delay while the user is writing. However, actually, a time delay of about 0.5 seconds occurs, so the user may feel irritated while writing.
The other reason is associated with a character recognition error. According to conventional character recognition technology, characters are recognized at an accuracy of about 90% in an actual situation. Even this accuracy can be accomplished only when various interface assistant devices for easily distinguishing characters are provided. When an error occurs while a user's writing is continuously recognized and processed, the user acts to correct the error, which disturbs continuity.
To overcome these problems of the character recognition technology in the field of pen interface, an approach which uses digital ink, i.e., a trace of a digital pen, without a character recognition procedure for determining an ASCII code corresponding to input digital ink has been proposed. As shown in FIG. 1, a detected pen's trace is stored in a digital form and displayed as it is so that a user can obtain information that he/she recorded. This method does not disturb the user's natural hand motion in writing down since character recognition is not performed. As a result, problems of the character recognition technology can be overcome.
However, in the above-described approach, since coded characters that can be recognized by a computer are not stored, the user needs to personally check all recorded information to search for desired information. To overcome this problem, a technique of searching for a medium recorded in the form of digital ink is required. According to such technique (hereinafter, referred to as a “digital ink search technique), when a search query in the form of digital ink (hereinafter, referred to as a “query phrase”) is input as shown in FIG. 2 in a situation where a plurality of memos recorded in the form of digital ink as shown in FIG. 1 (hereinafter, referred to as “memos”) are present, memos including the content of the query phrase are displayed as a search result.
Conventional methods for digital ink search premise that a search unit is a word separated from other characters or that a gap between recorded words is sufficient to divide characters in word units.
When words are distinctly separated from each other in a query phrase and memos, a search can be easily processed by comparing similarities between the query phrase and memos using a method such as elastic matching disclosed in various existing documents. In this situation, since an object to be searched for is distinct, there is no problem in dividing characters into words, and speed does not matter. The elastic matching is well introduced by C. C. Tappert [“Cursive Script Recognition by Elastic Matching”, IBM J. Research Development, V. 26, No. 6, pp. 765-771, 1982]. In this method, two objects are compared with each other, and a degree of similarity between the two objects is expressed by a numerical value.
However, actually, in most digital devices having a small input screen, characters and words are not sufficiently spaced to be easily separated from each other since a user usually inputs characters without spacing words due to restriction in space. Even when space is sufficient to input desired information, some users do not strictly space words. In such a situation where a search object cannot be easily identified, there exists a problem of determining a part of a memo to be compared with a query phrase.